The invention, in accordance with the preamble of Claim 1, pertains to a pressure control valve with a control piston that can be displaced in a valve bore.
The control piston of pressure control valves according to the state of the art is held in its normal position by an energy storage device. In one direction of travel, the pressure control valve connects a pump connection to a load connection. In the other direction of travel, the pressure control valve connects the load connection to a tank connection while disconnecting the pump connection. If the pressure at the load connection exceeds a be predetermined set point, the control piston travels against the force of the energy storage device and thus reduces the flow cross section between the pump connection and the load connection until the pressure at the load connection corresponds to the predetermined set point. If the set point is exceeded, the control piston travels against the force of the energy storage device to such an extent that pressure is released from the load connection to the tank connection.
In known pressure control valves, it is disadvantageous if control instabilities occur during rapid control processes, due to the spring-mass system, in particular, within the region of the control piston.
DE 35 05 377 C2 discloses a pressure control valve in which a control piston that can be moved by an electromagnet is displaceably arranged in an axially closed distributor housing. DE-OS 27 00 058 discloses a flow control valve in which a plunger piston, which can be axially displaced in a bore in the control piston and forms an annular gap with the bore, forms a damping device for the movement of the control piston.
The invention is based on the objective of making available a pressure control valve that also guarantees a reliable and stable operation over a wide control range. The design costs for preventing the instabilities should be held to a minimum, and the individual components of the pressure control valve should be low in number.
The objective is realized with the pressure control valve disclosed in Claim 1. Special embodiments of the invention are disclosed in the subordinate claims.
According to Claim 1, the invention is based on a pressure control valve with a control piston that can be displaced in a valve bore; in one travel direction, said control piston connects a pump connection to a load connection under the effect of an energy storage device In the other travel direction, it connects the load connection to a tank connection while disconnecting the pump connection. The invention is characterized by the fact that a volume flow between the control piston and the valve bore, in particular, a volume flow in an annular gap formed by the control piston and the valve bore, causes a damping of the excursion movement of the control piston independently of the direction of travel of travel. The volume flow is preferably small, specifically, it is only as large as is required for the damping.
The advantages of the invention are that the damping is realized with an annular gap formed directly in the pressure medium channel, and that the damping volume is linked to the pressure medium volume flow. In addition, the arrangement has no dead volume with respect to the damping effect. These advantages become particularly evident in directly controlled pressure controllers, in which the damping options are basically limited.
The damping of the control piston by means of the volume flow and the respective pressure build-up associated therewith also provides the advantage that the damping effect is a function of the speed of the control piston and is due to the portion of the frictional forces caused by the entrained flow or displacement flow, and that the damping effect is a function of the differential pressure between the pump connection and the load connection and is due to the portion of the frictional force which is caused by the leakage flow from the pump connection to the load connection. This results in a particularly advantageous damping and control behavior of the pressure control valve. The portions of the leakage flow and the entrained flow or displacement flow can be adjusted in a particularly simple and advantageous fashion by correspondingly adapting the geometrical shape of the pressure control valve, in particular, the control piston. Since the frictional forces act on the outer surface of the preferably cylindrical control piston, a particularly uniform force effect and consequently a particularly superior control and damping behavior of the pressure control valve can be achieved.
The special embodiment of the invention according to Claim 2 provides the advantage that the direction and the amount of the entrained flow can be predetermined. In this case in particular, it can be predetermined that the entrained flow is introduced into the pressure control valve at the load connection which is usually subjected to a lower pressure than the pump connection.
The special embodiments of the invention according to Claims 3 and 4 provide the advantage that a hollow cylindrical volume, into or from which the entrained flow or displacement flow which passes through the larger annular gap at the load connection can be introduced or discharged, respectively becomes larger or smaller due to the step formed between the two sections of the control piston which have different diameters during the axial travel of the control piston between the step of the control piston and the corresponding step of the valve bore. Due to the geometrical design of the steps as well as the annular gap, the damping characteristic of the pressure control valve can be easily and precisely adjusted as well as adapted to different situations. For example, the control and damping characteristic of a pressure control valve can be changed by exchanging the control piston.
The special embodiment of the invention according to Claim 6 provides the advantage that coil springs represent reliable and inexpensive energy storage devices which have a long service life, and that coil springs are available with nearly any desired dimensions. As an alternative to coil springs, other mechanical energy storage devices, e.g., a leaf spring, an elastic element, or pneumatic or hydraulic pressure reservoirs may be considered for this purpose.
The special embodiment of the invention according to Claim 7 provides the advantage that a reliable connection between the load connection and the pump connection and between the load connection and the tank connection can be produced with simple and inexpensive structural means.
The special embodiment of the invention according to Claim 9 provides the advantage that a clear structural separation between the load connection, the pump connection and the tank connection is ensured. In this case, the pump connection and the tank connection may be realized radially or annularly.
The special embodiment of the invention according to Claim 10 provides the advantage that the control pressure or the set point can also be changed after the manufacture of the pressure control valve, even after the pressure control valve is installed into a larger system.
The special embodiment of the invention according to Claim 11 provides the advantage that the pressure control valve can also be easily installed and replaced in larger pressure control systems modularly, due to the use of the pressure control valves in the form of screw-type cartridges.
Additional advantages, characteristics and details of the invention are disclosed in the subordinate claims as well as the following description, in which one embodiment of the invention is described in detail with reference to the figure. In this respect, the characteristics disclosed in the claims and in the description may be essential for the invention individually or in arbitrary combination.